The UNESCO lists potential threats to underwater cultural heritage. One threat is chemical activity:
Chemical processes can disturb the integrity of a submerged archaeological site, as for instance the corrosion of iron and other metals, which augments with the availability of oxygen on a site. Also, bacteria activity on wood can form minerals, such as pyrite, which is detrimental to wood because of the low PH3 which causes hydrolysis of the cellulose. Several important ships recovered from the seabed such as the Vasa, the Mary Rose or the Batavia have suffered damage as a result of such processes. Abnormal waves produced by underwater earthquakes can also disrupt the equilibrium of a site, removing the sediment over it and exposing it to water or bacteria. Many sites are also exposed to air due to sea level changes and may in consequence be destroyed.